The present invention relates to a polyolefin composition with extremely little odor containing vegetable fibers mainly composed of cellulose fibers.
Since polyolefins such as polypropylene have excellent mechanical properties and moldability, they are widely used for injection molding, extrusion molding, etc.
In order to improve the mechanical strength of such polyolefins, various fillers and additives are added thereto. Particularly to improve the mechanical strength, workability and dimension stability thereof, the addition of cellulose fillers such as pulverized wood chips, pulps, sawdust, rice hulls and used papers was proposed. For instance, Japanese Patent Laid-Open No. 60-158236 discloses polyolefin resin composition comprising a polyolefin resin containing chemically modified polyolefin and vegetable fibers mainly composed of cellulose fibers.
Among the above cellulose fillers, used papers and paper scraps are particularly advantageous as fillers for polyolefin compositions because of their low costs.
It has been found, however, that the incorporation of such cellulose fillers into polyolefins provide the resulting moldings with intolerable odor. The reasons therefor are not necessarily clear, but it may be considered that because of heat generated when polyolefins and fillers are blended and molded, the used papers or paper scraps are decomposed to generate aldehydes, alcohols, organic acids, ketones, etc. It is known as a deodorizing method to evacuate a molding machine through vent holes while molding polyolefin compositions to withdraw smelling materials to the outside, or to add a small amount of water simultaneously with charging the polyolefin compositions into the molding machine to withdraw the smelling materials to the outside together with steam. These methods, however, fail to provide molded products of acceptable odor level.